Yeah. I don't know of any tasks. It's not done, but it seems fairly easy
– all the pieces are there and they just need to be connected. ChangeTags::buildTagFilterSelector() already has an option to return
an OOjs UI widget, so HTMLTagFilter just needs to have a getInputOOUI() method added that would call that and return the widget.

Ok, the recent version I uploaded changed the changetag filter a bit, so that it suggests the filter, which are currently available, insteaad of requireing the user to type the tag in. However, because of recentchanges in the form, there's one more form element, which does not support OOUI: